RFID systems - antenna system and software method to spatially locate transponders

ABSTRACT

Apparatus and methods for locating an RFID transponder in space is described. The invention includes an RFID transponder for broadcasting identification data and a plurality of antenna for receiving identification data broadcast by the RFID transponder. The plurality of antenna are associated with the plurality of support members or shelves and control circuitry connected to the plurality of antenna determines which of the plurality of antenna receives identification information broadcast from the RFID transponder to determine the location of the transponder.

FIELD OF THE INVENTION

[0001] The present invention relates to the use of RFID transponders,and more specifically, to locating or finding a specific product orpackage carrying or incorporating an RFID transponder having a uniqueidentification number and that is stored on a plurality of verticallyand/or horizontally spaced shelves. Each of the shelves having at leastone loop antenna for interrogating RFID transponders.

BACKGROUND OF THE INVENTION

[0002] RFID transponders are now being used extensively for inventorycontrol, products and packaging in commercial settings. The availabletransponders include complex battery powered and long range expensivetransponders which may be attached to valuable one-of a-kind products,products which are limited in number, or products which are so expensive(on the order of hundreds or thousands of dollars) that they can justifysubstantial costs for protection. Such higher end transponders may bepart of a theft protection system which actually contacts a police typemonitoring service and/or which cooperates with some type of positioningsystem, such as for example, GPS (Global Positioning Satellite). Suchpositioning systems provide a continuous indication of the transponder'slocation, and of course, the product to which the transponder isattached. At the other end of the spectrum are the inexpensive (cost pertransponder in pennies or less) tuned antennas routinely attached topackages or products in department stores that will set off an alarm ifa customer passes through or is in close proximity to a detector usuallypositioned at an exit. These antennas are all substantially identicaland cannot provide a unique identification code.

[0003] The present invention, however, is primarily for use with an RFIDtransponder that provides unique identification codes for eachtransponder in the same manner the more expensive transponders. At thesame time, these transponders do not require a battery or other powersupply, and the cost is in the range of about $1.00 per transponder orless. Transponders specifically suited for use with this invention areavailable from Texas Instruments Incorporated under the trade nameTIRIS®. One such transponder is described in U.S. Pat. No. 5,053,774 toJosef H. Schuermann, and assigned to Texas Instruments.

[0004] According to one embodiment, a suitable transponder for use withthis invention will absorb sufficient energy from an interrogatingantenna to allow the transponder to transmit the necessary identifyinginformation or codes. In addition, the transponder should also operatesatisfactorily when there are more than one interrogating antennas. Onceexample of a transponder interrogation protocol for use in amulti-interrogator field is discussed in U.S. Pat. No. 5,646,607 alsoissued to Schuermann, et al., and assigned to Texas Instruments. U.S.Pat. No. 5,729,236 issued to Thomas J. Flaxal and assigned to TexasInstruments discloses a related patent entitled “Identification SystemReader with Multiplexed Antennas.” Similarly, U.S. Pat. No. 5,294,931issued to H. Meier and assigned to Texas Instruments discloses a “Methodof interrogating a Plurality of Transponders Arranged in theTransmission Range of an Interrogating Device.”

[0005] As will also be appreciated by those skilled in the art, if thereis a large number of transponders that may respond to a singleinterrogation attempt, it is important to have some sort of“anti-collision” hardware or software protocol to assure alltransponders report. U.S. Pat. No. 5,489,908 entitled “Apparatus andMethods for Identifying Multiple Transponders,” U.S. Pat. No. 5,500,651entitled “System and Method for Reading Multiple Transponders,” and U.S.Pat. No. 5,793,324 entitled “Transponder Signal Collision AvoidanceSystem,” all assigned to Texas Instruments provide related information.

SUMMARY OF THE INVENTION

[0006] Objects and advantages of the invention will in part be obvious,and will in part appear hereinafter, and will be accomplished by thepresent invention which provides methods and apparatus for locating anRFID transponder in space. The invention comprises one or more RFIDtransponders for broadcasting identification data. A plurality ofantenna suitable for receiving the identification data which isbroadcast by the transponders are associated with support members suchas shelves which are positioned at known vertical locations. There is atleast one antenna associated with each of the support members orshelves, and there typically may be two or more such antennas arrangedside by side on each such shelf or support member. The support membersor shelves support products or packages that include or have one of theRFID transponders attached thereto. According to a preferred embodiment,the RFID transponders do not include their own power supply and absorbor store power that is provided by the interrogation antennas. There isalso included control circuitry connected to the plurality of antennasfor determining which of the antennas receive the identificationbroadcast data that is broadcast from one or more of the RFIDtransponders. The transponders usually have rather short broadcastdistances so that only those antenna which are within approximately twoor three feet of the transponder will receive the identification data.Of course, depending on the application, transponders with shorter orlonger range would be appropriate. The control circuit also determinesthe location of the RFID transponder as a function of the antennas whichreceive the information data and as a function of the support members orshelves which are associated with receiving the information data. Also,according to a preferred embodiment, the antennas are preferably flat orloop antennas which lie substantially in the plane of the shelf orsurface of the support member.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The above-mentioned features as well as other features of thepresent invention will be more clearly understood from the considerationof the following description in connection with the accompanyingdrawings in which:

[0008]FIG. 1 is a schematic representation of vertical and horizontalspaced antennas for determining the three-dimensional location of anRFID transponder.

[0009]FIG. 2 is a flow diagram of the method of the present invention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

[0010] Referring now to FIG. 1, there is shown a schematicrepresentation of the apparatus incorporating the features of thepresent invention. As shown, a bottom row 10 includes a shelf 12 havinga series of antennas 14 a, 14 b-14 n, all mounted side by side such thatthey are substantially coplanar with shelf 12. Antennas 14 a, 14 b and14 n, will typically be loop antennas which are attached to the bottomor the top of the shelf 12 such that the loop of the antenna issubstantially coplanar with the shelf surface. There is also, a secondrow 16 having a shelf 18 which also includes a series of side by sideloop antennas 20 a, 20 b-20 n. Likewise, there is a top row 22,including shelf 24 having a series of loop antennas 26 a, 26 b-26 n. Aswill be appreciated by those skilled in the art, the series of stackedshelves 10, 16 and 22 may represent storage shelves or even displayshelves in a commercial or retail establishment. Shelves 28, 30 and 32along with loop antennas 34, 36 and 38 illustrate another stacked row ofshelves at a different location in the establishment. Likewise, shelves40, 42 and 44 having loop antennas 46, 48 and 50, respectively, alsorepresent another location of stacked shelves. Diagram 52 in theschematic of FIG. 1 illustrates the horizontal dimension X, and thevertical dimension Z. It will also be appreciated by those skilled inthe art, it is possible to also include a second horizontal dimension Yaccording to the teachings of this invention if it would be acceptablefor products and shelves to be stacked two deep. That is, at multiplelocations along the Y axis. However, for ease of understanding only, theembodiments discussed will assume a multiplicity of antennas in thevertical or Z direction, and a multiplicity of antennas in the Xdirection. To also include antennas for reading products in the Ydimension, it will be only necessary to add additional antennas in thatdimension. Also as is shown, the shelves 10, 16 and 22, as well as theshelves 28, 30, 32, 40, 42 and 44 are all connected to a multiplexingcircuit 54 which is in turn connected to a computational circuit 56 andinterrogation circuit 58. These circuits comprise the control circuitryfor the apparatus.

[0011] As was discussed above, each of the shelves has one or moreantennae associated therewith. The antennae are typically loop antennaswhere the plane of the loop coincides with the plane of the shelf. Theantennae are suitable for operating with an RFID interrogator, and therewill be as many antennae in a specific shelf as the number of locationsin the horizontal direction that need to be distinguished. Thus, in theexamples given, shelf 18 in middle row 16 contains loop antennas 20 a,20 b-20 n. And as will be appreciated, the letter “n” represents anysuitable or selected number. As shown, the size and shape of each of theantenna is such that it will approximately cover the required area ofeach location that is to be identified. Further, in the embodimentshown, each shelf or row has a set of antennas that is similar ormatches the sets of antennas in the other shelves or rows. For example,there are antennas 20 a and 26 a associated with shelves 18 and 24 whichmatch antenna 14 a on shelf 12 of bottom row 10. Thus, as will bediscussed hereinafter, this arrangement allows any two antennas that arevertically adjacent to be designated as an interrogation pair.Multiplexer 54 operates to select a pair of vertically adjacent antennasuch that an RFID interrogation can take place with each of the selectedpairs. For example, one selected pair selected by the multiplexer 54could be antennas 14 a and 20 a which are located in shelves 12 and 18,respectively. Likewise, another pair of antennas selected by multiplexer52 may be antenna 20 a and antenna 26 a located in shelves 18 and 24,respectively. Thus, it is seen that a single antenna may be a member ofmore than one interrogation pair. As was mentioned heretofore, there maybe more than one transponder located in close proximity to each antennalocation on a shelf. For example, location of antenna 20 a on shelf 18includes a plurality of products each containing a separate transponder60 a, 60 b-60 n. Thus, if antennas 20 a and 26 a are selected as a pairfor interrogating transducers, it will be appreciated that each of thetransponders 60 a, 60 b-60 n may try to respond in which situationcomputer 56 and interrogator 58 must include some sort of anti-collisionprotocol. Collision avoidance protocols such as described in U.S. Pat.Nos. 5,489,908; 5,500,651, and 5,793,324 incorporated herein byreference are well-known in the art and therefore will not be discussedfurther.

[0012] Also as shown, individual transducers 62 a, 62 b and 62 c may belocated on single or individual products one to a shelf or one to anantenna location. It will be appreciated that it is often desirable touse transponders with limited range such as about one or two feet oreven less to avoid them being read by many of the adjacent antennas.Even so, if a pair of antennas such as antennas 20 b and 26 b areselected to read as an interrogation pair, it will be appreciated thatthese two antennae will certainly read transponders 62 b and 62 c.Transponder 62 b is almost directly in contact with antenna 20 b andtransponder 62 c is almost in contact with antenna 26 b. Likewise, ifantenna pairs 14 b and 20 b are selected, the two antennas making upthis pair will certainly read transponder 62 a and 62 b. Further, asmentioned, it may be desirable that the RFID transponder be selected ortuned to have a short enough reading range so they will not be readexcept by two or three of the closest antennas. However, this is notalways possible and sometimes conditions will be such that a largenumber of surrounding antennas may read a single transponder. Forexample, in the embodiment shown, transponder 62 b is indicated byradiation lines 64 a-64 g as having sufficient transmission power to beread by at least nine separate antennas. Thus, it will be appreciatedthat if a single transponder or the package attached to which thetransponder is attached is to be located by the control circuitry withrespect to its vertical and horizontal position on a shelf, it can onlybe assumed that the transponder is located on one of the nine shelves.Consequently, there must be some protocol available for determining thelocation of the particular transponder in view of the multiplicity ofreadings. A suitable protocol or algorithm for determining this isdiscussed hereinafter.

[0013] From the embodiment illustrated in FIG. 1, it can also be seenthat there may be a single antenna for each shelf as shown with respectto shelves 28, 30 and 32. Such an arrangement would be perfectlysatisfactory for large items which can not include two products side byside on a single shelf. It should also be appreciated that thearrangement of shelves and antennas offers many choices depending uponthe particular use and size of the products being stocked.

[0014] As was discussed above, it is desirable to have a protocol oralgorithm whereby computer circuitry 56 can more precisely identify thelocation of each transducer. Thus, referring now to FIG. 2, there isshown a flow diagram suitable for determining the location of atransducer even if multiple antennas read the same transducer. As shown,there is a first step or block 70 wherein the various antenna pairs areidentified and have their locations stored at known X (horizontal) and Z(vertical) locations. It is noted, as discussed above, for more complexsystems, there could also be included a Y location storage. Then at step72, each antenna pair is used to interrogate transponders within readingrange and will list each unique transponder read by that antenna pair.As shown in step 74, the algorithm will then determine whether or notmore than one transponder appears with respect to more than one pair ofantennae. If the answer is NO, then the location both vertical andhorizontal of the antennas which read the specific transponder,represents the closest location of the interrogated transponder, and thealgorithm skips to step 88. However, as discussed, the answer willusually be YES, there is more than one pair of antennae or list uponwhich a transponder appears. Therefore, the program proceeds to step 76,which assigns the X and Y location values of the antenna reading thetransponder. This is done for each listing of a specific transponder.Then as shown at step 78, the average X and Y values of all of theantennae reading a specific transponder are determined. The algorithmthen progresses to step 80, wherein a determination is made as towhether or not the antenna which read the transponder is on the topshelf. If the answer is YES, the location of the average shelf locationof the transponder is rounded down to the next lower shelf. However, ifthe answer is NO, the question is asked at step 84 whether or not theantenna is on a bottom shelf. In the case where the answer is YES, thelocation is rounded up to the shelf above the bottom shelf. However, ifthe answer is NO, then the program progresses to step 88 whichdetermines if the average value is exactly between two integral values.If the answer to the determination of step 88 is NO, then the locationof the read transponder is rounded up or down to the closest value asthe location as shown at 90. On the other hand, if the answer is YES,then the location of the shelf is considered to be divided in a top halfand a bottom half as indicated at step 92. The program then progressesto step 94 wherein there is a determination made as to whether or notthe average location is in the top half of the divided shelf. If so, thevalue of the shelf is rounded up as the location as indicated at 96.Whereas, if the answer is NO, the shelf is rounded down to the lowerlocation as indicated at 98.

[0015] Thus, there has been described a method for determining thelocation of a transponder that will yield a matrix of interrogationresults in which each antenna element represents a location in the shelfin both horizontal and vertical directions. A list is completed forevery element or antenna which includes unique transponder numbers(ID's) that resulted from the interrogation that takes place with eachantenna pair belonging to that location. Since It is possible that aspecific identification number can appear in more than one list, theabove-described algorithm determines the most likely real location ofeach transponder according to its identification number. It will also beappreciated that the same procedure can be used for determining thehorizontal location by averaging the horizontal values of each of theantenna on a shelf.

I claim:
 1. Apparatus for locating an RFID transponder vertical locationcomprising: an RFID transponder for broadcasting identification data; aplurality of antennae for recovering said identification data broadcastby said RFID transponder; a plurality of support members at spaced apartvertical locations suitable for supporting said RFID transponder, andeach of said spaced apart support members associated with at least oneof said plurality of antennae; and control circuitry connected to saidplurality of antenna for determining which of said plurality of antennareceives said identification broadcast from said RFID transponder andfor determining the location of said RFID transponder as a function ofthe antenna receiving said broadcast data and the support membersassociated with the antennae receiving said identification data.
 2. Theapparatus of claim 1 wherein at least two transponders broadcastseparate identification data.
 3. The apparatus of claim 1 wherein saidantenna or loop antennas and the plane of the loop of the antenna issubstantially coplanar with said support member.
 4. The apparatus ofclaim 1 wherein each of said support members includes at least twoantennae located side by side, and wherein both the vertical andhorizontal location of the transponder is determined.
 5. The apparatusof claim 1 wherein said RFID transponders are attached to a product orpackage.
 6. The apparatus of claim 1 further comprising a multiplicityof products or packages and a multiplicity of RFID transponders, eachtransponder for broadcasting different identification data, and at leastone each associated with said multiplicity of products or packages. 7.The apparatus of claim 1 wherein said support members at known verticallocations are a plurality of shelves stacked vertically.
 8. Theapparatus of claim 7 wherein each of said shelves has two or morehorizontal locations for supporting products or packages to which atransponder is attached, each shelf has an antenna corresponding to saideach of said horizontal locations, and wherein both the vertical andhorizontal location of the transponder is determined.
 9. The apparatusof claim 1 and further including a multiplexer connected between saidcontrol circuitry and said plurality of antennas for selecting a pair ofadjacent antennas.
 10. The apparatus of claim 1 wherein said RFIDtransponder stores power transmitted by one or more of said antennas foruse to provide said transmitted identification data.
 11. The apparatusof claim 1 and further comprising computer circuitry for averaging thevertical location of antennae reading said transponder.
 12. A method oflocating an RFID transponder in space comprising the steps of:broadcasting identification data from an RFID transponder; receivingsaid broadcast identification data at a plurality of antenna; providinga plurality of spaced apart support members at known vertical locationssuitable for supporting said RFID transponders, and each of said spacedapart support members associated with at least one of said plurality ofantennas; determining which antenna receive identification databroadcast from said RFID transponder; and determining thethree-dimensional location of said transponder broadcasting saididentification data as a function of the antennas receiving saidinformation data and the support members associated with the antennasreceiving said identification data.